In end-to-end coupling of two optical fibers, the closer together the two fiber ends can be brought together and aligned on their common center-line, the less light or power is lost. In connectors for such end-to-end coupling having ferrules to retain the optical fibers, the cleaved end of an optical fiber is initially just flush with the end surface of the ferrule. Thereafter, when the rear portion of the retainer sleeve of the ferrule is crimped to the jacket of the optical fiber cable, the cleaved end of the optical fiber may recede away from the face of the ferrule and against which the face of the second ferrule housing the second optical fiber would abut. Such a connector assembly is referred to in U.S. Patent Application Ser. No. 698,392, entitled "Fiber Optic Connector", filed June 21, 1976 by Earl R. Heldt. In that connector, the cleaved end of the optical fiber recedes from the face of the ferrule. Hence, a gap between the cleaved ends of the fibers to be coupled results during assembly of the outer jacket of the optical fiber cable to the end of the ferrule sleeve.
In addition, the cost of the split, outside threaded sleeve as shown in the above-referenced patent application and into which the connector of the two fibers to be connected is inserted, is high owing to the machining required to hold the close tolerance of the inside diameter. Typically the tolerances of the inside diameter of the outside threaded sleeve and the ferrule were not adequate to maintain fiber-to-fiber concentricity. To improve alignment tolerance and to maintain production costs, the sleeve was slit in order to allow it to act as a spring and take up the clearance between its inside diameter and the ferrule outside diameter. However, the amount of force the spring developed in this approach was unpredictable. To improve predictability of fiber alignnment, a double leaf spring was machined into the sleeve as also described in the above-mentioned patent application, while improvement was achieved the cost was high. The present invention abandons the use of slits and leaf springs in favor of an outside threaded sleeve having a uniform inside diameter into which a shim sleeve of molded, pliable material having a "D"-shaped inside diameter is slip-fit therein. The inside diameter of the shim sleeve acts as a spring on the outside diameter of the connector ferrules.